The invention relates to an aircraft air conditioning system with an electrically driven ambient air compressor and a method for operating such an aircraft air conditioning system.
In commercial aircraft, so-called air-based air conditioning systems, such as are described, for example, in DE 10 2008 053 320 B4 and U.S. Pat. No. 8,333,078 B2 or EP 2 651 763 A2 and US 2013/269327 A1, are normally used at present for air conditioning of the aircraft cabin. An aircraft air conditioning system is used to set and maintain a desired pressure, desired temperature and desired air humidity in an aircraft cabin. Moreover, the aircraft air conditioning system supplies adequate fresh air to the aircraft cabin to ensure that a prescribed minimum quantity of fresh air is present in the aircraft cabin. Finally, the aircraft air conditioning system ensures that the aircraft cabin is kept at a desired pressure, which is increased compared with the ambient pressure at the flight altitude of the aircraft, in flight mode of the aircraft.
Air-based aircraft air conditioning systems normally comprise an air conditioning unit, to which compressed process air is supplied by the engines of the aircraft, a separate compressor or an auxiliary power unit (APU). In flight mode of the aircraft, engine bleed air is mainly used to provide the air conditioning unit of the aircraft air conditioning system with compressed process air. In ground operation of the aircraft, the air conditioning unit of the aircraft air conditioning system is normally supplied, on the other hand, with compressed process air from the auxiliary power unit or an aircraft-external air generating unit. In the air conditioning unit, the process air is cooled and expanded on flowing through at least one heat exchanger unit as well as various compression and expansion units. Cooled process air exiting the air conditioning unit is finally conducted into a mixing chamber and is mixed there with recirculation air removed from an aircraft area to be air conditioned. The mixed air from the mixing chamber is conducted via corresponding mixed air lines into the aircraft area to be air conditioned, which can be in the form of a passenger cabin, a cockpit, a cargo hold, a crew rest room or similar and divided into several climate zones.
DE 10 2010 034 830 A1 and WO 2012/022758 A1 describe an aircraft air conditioning system in which the compressed process air, which is taken from an engine of the aircraft, is cooled by the transfer of heat to a coolant flowing through a cooling circuit. A turbine, which serves to expand the compressed process air before it is supplied to an aircraft cabin, is used to drive a compressor arranged in the cooling circuit.